Thermostat or the like having twisted bimetal strip therein

ABSTRACT

In this thermostat, thermal protector, or the like, a casing has at least one initially open end and a bimetal strip extends into the casing as a cantilever, being positioned thereby by insulation means securing the strip in position and sealing the initially open end of the casing. The strip has layers of different metals on the top and bottom surfaces thereof, and the strip has about a 180* twist therein intermediate the secured portion and the free end portion thereof whereby improved cycling in the thermostat is obtained.

United States Patent Wells 1541 THERMOSTAT on THE LIKE HAVING TWISTED BIMETAL STRIP THEREIN [72] Inventor: Alton R. Wells, 4573 West Trade Winds Avenue, Lauderdale-by-the-Sea, Fla. 33308 [22] Filed: Apr. 29, 1970 [21] Appl.No.: 32,955

[52] U.S.Cl ..337/lll, 73/3635, 337/107 [51] lnt.Cl ..H0lh 37/52, HOlh 61/01 [58] Field ofSearch ..337/38, 39, 40, 89, 92, 95,

337/96,99,100,10l,l02,103,l07,11l,112, 336, 337, 370, 371, 378, 379, 380; 73/3635 [5 6] References Cited UNITED STATES PATENTS 3,033,958 5/1962 wens etal 3 sy g ugg 3,656,080 [4 1 Apr. 11, 1972 1,938,929 12/1933 Peterson ..73/363.5X 3,307,001 2/1967 Alban ..337/379X Primary ExaminerBemard A. Gilheany Assistant ExaminerDewitt M. Morgan Attorney-Oldham & Oldham 7] I ABSTRACT In this thermostat, thermal protector, or the like, a casing has at least one initially open end and a bimetal strip extends into the casing as a cantilever, being positioned thereby by insulation means securing the strip in position and sealing the initially open end of the casing. The strip has layers of different metals on the top and bottom surfaces thereof, and the strip has about a 180 twist therein intermediate the secured portion and the free end portion thereof whereby improvedcycling in the thermostat is obtained.

9 Claims, 8 Drawing Figures PATENTEDAPR 11 I972 3,656,080

SHEET 2 OF 2 FIG.6

I INVENTOR. ALTON R. WELLS 6%? www ATTORNEYS.

THERMOSTAT OR THE LIKE HAVING TWISTED BIMETAL STRIP THEREJIN The novel thermal protector, thermostat or equivalent article of the invention is particularly designed to have a controllable, and slower cycle rate than that of similar cantilever type bimetal thermostats.

In the various control functions obtained by previous types of thermostats or other thermal protectors in industry, in some instances it is very desirable to have a relatively rapid on-off cycle for the thermostat and the on and off times in such cycles can be varied in some control articles as heretofore made. However, most of these cantilever types of thermal controls as made heretofore have not been able to provide slow operating cycles with temperature differentials in the thermostat between the open and the closed conditions for the thermostat or other article and the circuit controlled thereby.

The general object of the present invention is to provide a novel and improved thermal protector including a bimetal cantilever strip positioned in a thermostat casing and wherein the bimetal strip has a substantially 180 twist therein intermediate the secured portion thereof and the free end of the cantilevered section of the strip whereby reverse bending action occurs in the two portions of the cantilever section of the strip and improved control actions can be obtained therein. Another object of the invention is to provide a thermal protector wherein reverse bending conditions are provided in a cantilevered bimetal strip in different portions or sections of the cantilevered length of the strip and wherein the free end portion of the strip is curved by heat to move towards a contact on the thermostat casing whereby no contact opening action will occur until after such bimetal end portion is appreciably' curved towards an associated contact.

A further object of the invention is to obtain a relatively slow cycle thermostat wherein the cycle rate and the temperature variation between open and closed conditions can be controlled by the location of substantially a 180 twist in the cantilevered portion of the bimetal strip.

The foregoing and other objects and advantages of the invention will be made more apparent as the specification proceeds.

Reference now is made to the accompanying drawings, wherein: thermostat cantilevered bimetal FIG. 1 is a vertical section through a thermostat embodying the principles of the invention indicating a cantilevered bimental arm as the contacts are opening;

FIG. 2 is a fragmentary horizontal section taken on line 2- 2 of FIG. 1;

FIG. 3 is a vertical section through a modified embodiment of the invention;

FIG. 4 is a plan view of the bimetal strip of the thermostat of FIG. 1 prior to providing the twist in such strip;

FIG. 5 is a plan of a modification of the strip of FIG. 4;

FIG. 6 is a longitudinal section of a modification of the invention, the contacts being closed;

FIG. 7 is a section of a further modification of the invention; and

FIG. 8 shows the thermostat of FIG. 7 with its contacts open.

When referring to corresponding members shown in the drawings and referred to in the specification, corresponding numerals are used to facilitate comparison therebetween.

Attention now is particularly directed to the details of the structure shown in the drawings and a novel and improved thermostat or thermal protector of the invention is indicated as a whole by the numeral 10. This thermostat 10 includes a conductive case 11 which initially normally has one open end 12 provided therein. A bimetal strip 13 is secured in the initially open end 12 of the casing 11 by conventional means such as a fiberglass-resin impregnated sleeve 14 or equivalent means positioned around the bimetal strip 13 and suitably sealed in relation to the strip 13 and the initially open end of the casing 11, all in a conventional manner whereby the major portion of the bimetal strip 13 extends into the casing 11 normally towards the closed end thereof and is positioned as a cantilever within the casing 11. Any suitable terminal means and/or leads can connect to the casing 11 and the bimetal strip 13 in a conventional manner forconnecting a circuit to the thermostat 10 to be controlled thereby.

Usually a contact 15 is carried by the free end of the strip 13 and a contact 16 is secured to the inner wall of the casing to be positioned in opposed relation to the contact 15 for opening and closing the circuit to be controlled by the thermostat.

As a feature of the invention, the bimetal strip 13 is twisted through a substantially arc at a twist area 17 formed therein. This twist, or twist area 17 thus positions the bimetal forming the free end of the strip 13 in a different manner from the bimetal in the portion of the strip 13 adjacent the sealed or positioned end thereof. Hence, a free end reverse acting section 18 is provided in the bimetal strip 13 and a secured nor mal action base section 19 is formed in such bimetal strip 13. Normally the strip 13 is formed from top and bottom layers of metal whereby the vertically upper metal in the base section 19 of the strip 13 is different from the bimetal material which is on the upper portion of the end section 18 of the strip 13. Hence, if the base section 19 normally would move up under heating conditions, then the end section 18 moves downwardly under heating conditions, such as when an electrical current is flowing therethrough, or from external heating means.

It has been found that the provision of the twist area or zone 17 in the bimetal strip 13 is facilitated as by forming notches 20 as shown in the strip 13 of FIG. 4, which shows such strip prior to providing the 180' or approximately 180 twist therein. FIG. 5 shows a modified strip 30 having arcuately contoured notches 32 formed in opposed lateral margins thereof. It should be noted that the notches 20 and the notches 30 each can extend, at most, one-third of the lateral width of the strips 13 or 30 in which they are formed as any greater notching of the bimetal strips normally may form too hot an area at the notched and twisted section when current is conducted through such strips when the thermostats in which they are positioned are in use. By the provision of these notches 20, 32, or equivalents, in a bimetal strip, then the twisting of the strips is facilitated and the bimetals comprising the strips are not torn or otherwise injured for operative use in a thermostat. By the improvement of the invention, the thennostat 10 has been reduced, for example, to 22 cycles per hour while 'a similar thermostat with a conventional bimetal strip therein and under the same load had cycled seven times a minute.

The casing 111 may be conductive or not, as desired, and the contact 16 may have a lead extending therefrom to and through the open end of the casing. Both ends of the casing may be open, if desired, and the thermostat may have a second arm extending thereinto as shown, for example, in U.S. Pat. No. 2,586,309. The thermal protectors may be calibrated. as disclosed in U.S. Pat. Nos. 2,497,397 and 2,586,309. The sealed end or ends of the thermal protector may be of the construction disclosed in U.S. Pat. No. 3,209,107.

Preferably the bimetal strip has a 180 twist therein but minor or slight variations therefrom can be tolerated.

Any conventional bimetal strips may be used with the base section 19 normally having, for example, a layer 40 of high expansion metal such as a nickel-chrome-steel alloy, and a layer 41 of a low expansion metal, such as nickel-iron alloy therein. W.M. Chace Co. of Detroit, Michigan makes a number of known types of bimetals and its No. 2400 is typical of the strips in use today.

Some of the advantages resulting from the present invention include the following:

a. Purchase of bimetal strips and storage thereof is flexible as conventional straight laid bimetal strips can be converted into compound bimetal strips with a simple, single operation with minimum labor costs and no additional material costs.

b. The cycle rate in the thermostat can be controlled from a substantially normal cycle action rate in cantilever types of thermostats or the like, to an extremely slow cycle rate, such as from about five per minute to about one every 3 minutes by the location .of the twist in the cantilevered portion of the bimetal; and the opening temperature may, for example, be

, about 30? F. above the circuit closing temperature in ordinary operation, but there could be an 80 to 100 differential, if desired.

c. An increase of hot on time due to reverse action of the strip end carrying the contact.

d. Increased positiveness and speed of circuit opening action'due to the fact that the reverse acting bimetal is normally at a substantial deflection before opening'action takes effect and the reverse acting bimetal then starts to cool and move upward as no current is flowing therethrough, thus increasing the opening between the contact points.

e. Increased speed and/or positiveness of closing circuit contacts as any heat created at the contacts immediately causing the reverse acting bimetal to increase its closing velocity and/or strength.

f. Atendency of a contact are to reopen a normal straight blade bimetal strip is positively eliminated.

g. Obtain advantages'of a compound bimetal strip without the technical problems of making such compound bimetal strip and controlling the manufacture so that the product will meet the specifications therefor. Many bimetals are expensive and are not available commercially in short or small length sections.

In making the strip 13 of the invention and the end section '18 and base section 19 therein, usually the bimetals are so positioned in the base section 19 as to have an upwardly moving action under heating conditions, as indicated by the arrow 42, and the end section has the reverse or downwardly extending curving action under heated conditions. It also should be realized that the positioning of the bimetal materials in the strip 13 can be reversed whereby the base section 19 can be provided with a downwardly extending curving movement under elevated temperatures, whereas the end section 18 then would be provided with an upwardly directed curving action under heating conditions and this would appreciably change and alter the circuit opening and closing actions and the cycle rate of the thermostat. In the preferred construction of the invention, the advantages set forth hereinabove are particularly provided in a strip 13 that has an upwardly curving action in the base section 19..

FIG. 3 shows a modified thermostat 10a where a bimetal strip 13a is twisted at 17a and a heater strip 31 is suitably secured, usually welded, to the free end section 18a and extends axially therefrom. A contact 15a is secured to the heater strip 31 which may be made from any conventional material such as. brass or an lnconel, such as Inconel 320-7. Such a construction can increase the rate of deflection of the free end section of the heater strip. If Inconel is used, a higher electric resistance heating action is obtained and heat flows back to the short arm 18a to make it operate so that the contacts are opened at a relatively higher temperature than that secured by the action solely of the base section 13a of the bimetal strip, or by the strip 13. Hence, the hold in sensitivity of the thermostat in relation to an equivalent strip 13a without a heater strip 31 can be controlled, and higher opening temperatures can be obtained. A

FIG. 6 shows a thermostat 10b where two twisted bimetal strips 44 and 45 are provided. These strips extend into a casing 43 from two initially open ends thereof. These strips 44 and 45 can be of the construction of the strip 13 and will, normally, double the differential of a one arm thermostat as in FIG. 1.

By theimproved thermostat or motor protector, or thermal controls of the invention, an improved slow cycle thermostat control has been provided and found to, be very desirable in commercial use. By' the reduced cycles in a protected device,

such as in an electric motor, measurably greater operative point or contact life can be obtained, and more consistent action is obtained in the motor control function by the thermostat opening and closing circuit therefor at optimal tempera ture conditions for a much greater period of time. In fact, this design causes thetemperature cycle to be of greater repetitive consistency and predictability and in effect accomplishes the temperature control cycle pattern of the well known and highly used snap action thermostats, but with the temperature control action being provided at reduced manufacturing and selling costs to ultimate user. The embodiment of the invention also does not have the disadvantage of a snap action thermostat, namely mathematical probability of contact opening at the maximum point of the sine wave power which results in a maximum are potential. In addition, the amperage capacity of the thermostat is substantially increased and this is valuable in small or miniature controls.

In the thermostats of the invention,as the current increases, the heat at the twisted zone of the bimetal strip increases and tends to flow to the adjacent end of the section 18 of the bimetal strip. This aids in providing long cycles of operation in the thermostat, especially when short lengths, relatively speaking, are provided in the bimetal section 18. FIG. 2 shows that the base ann section 19 may have a length a" from the secured end portion thereof to the twist area and the free end section 18 has a length b" from the contact 15 to the twist area and with the twist area having a length c. Thus, the distance a may be, for example, from about V4 to inch, the distance or length b may be about l/32 to 5/16 inch, and the length c about 5/32 inch. It is preferred that the length of the arm section 19 a from its secured end thereof to the twisted area or zone would be about two to three times the length of the arm. section 18 or b. In making the twists in the bimetal strips, naturally it is desirable to avoid any tear of the metal and this twist does increase the strength of the bimetal strip and hence aids in increasing the operative strength of the produced unit. The thickness of these bimetal arms or stripsmay be, usually, about 0.010 to 0.12 inch, but may go as high as from 0.0l5 to 0.030 inch in some instances where heavy or large currents are involved. The strips, for example, may usually be about six times the thickness in width.

In view of the foregoing, it is submitted that an improved thermostat or thermal control has been provided that has very desirable properties and that such thermostat can be readily calibrated for different cycle rates by varying the axial location of the twisted area or zone 17 in relation to the contact The thermostat usually is of the circuit breaker type and has I a higher break temperature than the make temperatures for the circuit controlled by the bimetal arm or arms in the thermostat. This differential between opening and closing temperatures may be as low as 8 to 10.

The thermostats function fairly effectively on direct current but are particularly effective with AC to eliminate arcing in circuits with the slow lockrin action of the thermostat which in many instances may have a 600 to 1,000 watt capacity at or 240 volts.

FIG. 7 shows a novel thermostat 50 wherein one twisted bimetal arm 51 is provided and a conventional bimetal arm 52 is provided in this initially two open end type of a casing 53 whereby a further modified circuit control action can be obtained. The open position of the bimetal arms of the thermostat 50 of FIG. 7 is shown in FIG. 8 where an end arm section 55 is curved downwardly when the contacts are opened.

The thermostats are described as being horizontally positioned with the bimetal strip 13, for example, also being horizontally positioned or substantially so.

It also has been noted that the contacts as positioned and used in the thermostats described tend to have a wiping action between the semi-spherical surfaces of the contacts upon temand smooths thesurfaces thereof.

A new and improved thermal control is provided which has a substantial differential in opening and closing temperatures, and which has a slow cycle rate so that the objects of the invention have been achieved.

While several complete embodiments of the invention have been disclosed'herein, it will be appreciated that modification of these particular embodiments of the invention may be resorted to without departing from the scope of the invention.

What is claimed is:

1. A thermostat, thermal protector or the like connectable to an electric circuit comprising a casing having at least one open ed, a bimetal strip extending into the casing as a cantilever, insulation means securing said strip at the initially open end of said casing and sealing said open end and around said bimetal strip, and opposed contact means operatively positioned in said casing including one contact means on the free end of said bimetal strip for movement into and out of engagement with the other, contact means for circuit openings and closing action, characterized by said bimetal strip being of generally rectangular shape in section and having layers of different metals on the opposite longer surfaces thereof, said bimetal strip having a substantially 180 twist therein intermediate the ends thereof in a section of reduced width to form two axially spaced sections in said bimetal strip whereby different bending actions are obtained in said sections when heated, the secured end section of said strip being of the major length of the said strip and the free end section of minor length.

2. A thermostat, thermal protector or the like as in claim 1 where the major length is a relatively long axial section and the minor length is a relatively short axial section.

3. A thermostat, thermal protector or the like as in claim 1 where said bimetal strip has a notch provided on each side thereof at the twisted portion thereof.

4. A thermostat thermal protector or the like as in claim 3 where each notch extends into said bimetal strip up to one third the width thereof.

5. A thermostat, thermal protector or the like as in claim 1 where said bimetal strip has a heater metal strip secured to it at its cantilevered end, said heater strip projecting beyond said bimetal strip, and one of said contact means is secured to said heater.

6 A thermostat, thermal protector or the like comprising a conductive casing having at least one open end, a bimetal stn'p extending into the casing as a cantilever, insulation means securing said strip at the initially open end of said casing and sealing said open end and around said bimetal strip, and 0p posed contact means on said casing and the free end of said bimetal strip, characterized by said strip having layers of different metals on the vertically opposite surfaces thereof, said strip at the free end thereof having a different metal on the top surface thereof than at and adjacent the secured end thereof, said strip having a substantially 180 twist therein intermediate the ends thereof,

said strip adjacent the supported end thereof moves upwardly when heated and said strip at the free end thereof moves downwardly when heated whereby a circuit formed by the thermostat when said contacts engage is opened only after said free end portion curves downwardly to an appreciable extent; and

the open and close circuit cycle rate being controlled by the axial location of the twist in said strip in the cantilever portion thereof, the distance from the secured end of said strip to the adjacent edge of the twist being longer than the distance from the contact carried by the free end of the strip to the adjacent edge of the twist.

7. A thermostat as in claim 6 where the 180 reversed posi tion of the free end of the single bimetal strip results in a temperature of contact closing being significantly lower than the temperature of contact opening.

8. A thermostat, thermal protector or the like as in claim 6 where said stigp has a second metal strip secured to and proecttng beyon he cantilevered end thereof, and one of said contacts is secured to said second strip which is a heater strip.

9. A thermostat as in claim 6 where the position of the bimetal strip in relation to normal is reversed and the bimetal strip in the longer section thereof tends to curve toward a circuit closing position under heating conditions and wherein the temperature of contact closing is significantly higher than the temperature of contact opening and where the longer length section has the high expansion part of the bimetal on the opposite side thereof than that side to which the contact is attached. 

1. A thermostat, thermal protector or the like connectable to an electric circuit comprising a casing having at least one open ed, a bimetal strip extending into the casing as a cantilever, insulation means securing said strip at the initially open end of said casing and sealing said open end and around said bimetal strip, and opposed contact means operatively positioned in said casing including one contact means on the free end of said bimetal strip for movement into and out of engagement with the other contact means for circuit openings and closing action, characterized by said bimetal strip being of generally rectangular shape in section and having layers of different metals on the opposite longer surfaces thereof, said bimetal strip having a substantially 180* twist therein intermediate the ends thereof in a section of reduced width to form two axially spaced sections in said bimetal strip whereby different bending actions are obtained in said sections when heated, the secured end section of said strip being of the major length of the said strip and the free end section of minor length.
 2. A thermostat, thermal protector or the liKe as in claim 1 where the major length is a relatively long axial section and the minor length is a relatively short axial section.
 3. A thermostat, thermal protector or the like as in claim 1 where said bimetal strip has a notch provided on each side thereof at the twisted portion thereof.
 4. A thermostat thermal protector or the like as in claim 3 where each notch extends into said bimetal strip up to one third the width thereof.
 5. A thermostat, thermal protector or the like as in claim 1 where said bimetal strip has a heater metal strip secured to it at its cantilevered end, said heater strip projecting beyond said bimetal strip, and one of said contact means is secured to said heater. 6 A thermostat, thermal protector or the like comprising a conductive casing having at least one open end, a bimetal strip extending into the casing as a cantilever, insulation means securing said strip at the initially open end of said casing and sealing said open end and around said bimetal strip, and opposed contact means on said casing and the free end of said bimetal strip, characterized by said strip having layers of different metals on the vertically opposite surfaces thereof, said strip at the free end thereof having a different metal on the top surface thereof than at and adjacent the secured end thereof, said strip having a substantially 180* twist therein intermediate the ends thereof, said strip adjacent the supported end thereof moves upwardly when heated and said strip at the free end thereof moves downwardly when heated whereby a circuit formed by the thermostat when said contacts engage is opened only after said free end portion curves downwardly to an appreciable extent; and the open and close circuit cycle rate being controlled by the axial location of the twist in said strip in the cantilever portion thereof, the distance from the secured end of said strip to the adjacent edge of the twist being longer than the distance from the contact carried by the free end of the strip to the adjacent edge of the twist.
 7. A thermostat as in claim 6 where the 180* reversed position of the free end of the single bimetal strip results in a temperature of contact closing being significantly lower than the temperature of contact opening.
 8. A thermostat, thermal protector or the like as in claim 6 where said strip has a second metal strip secured to and projecting beyond the cantilevered end thereof, and one of said contacts is secured to said second strip which is a heater strip.
 9. A thermostat as in claim 6 where the position of the bimetal strip in relation to normal is reversed and the bimetal strip in the longer section thereof tends to curve toward a circuit closing position under heating conditions and wherein the temperature of contact closing is significantly higher than the temperature of contact opening and where the longer length section has the high expansion part of the bimetal on the opposite side thereof than that side to which the contact is attached. 